3
$\begingroup$

In the following table by A. Devoto and D. W. Duke, a number of logarithmic integrals are listed that - according to the authors - help with Feynman diagram calculations. In particular, integral (3.6.1) on p. 14 reads as follows: $$I := \int_{0}^{1} \frac{\ln(1-y)}{y} dy = - \zeta(2). $$ Here, $\zeta(\cdot)$ is the Riemann zeta function - and we have $\zeta(2) = \frac{\pi^{2}}{6}$.

Now, I am not a physicist, but a mathematician. I don't know how or when this integral exactly arises in Feynman diagrams and in quantum electrodynamics in general. My interest in this integral is mostly related to the following question I have on a particular quadratic rational zeta series. In that regard, I'm looking for integral expressions that amount to $$S_{k} := \sum_{i=1}^{k} \left[ {k \atop i} \right] \zeta(i+1). \tag{*} $$ In the above sum, the $\left[ {k \atop i} \right]$ are the unsigned Stirling numbers of the first kind.

Interestingly, we also have: \begin{align} I_{k} &:= \int_{0}^{1} \bigg{(} - \frac{\ln(1-y)}{y} \bigg{)}^{k} dy \\ &= k\sum_{n=0}^{k-1}\left[ k-1 \atop n\right]\zeta(k+1-n) . \tag{**}\end{align}

This expression comes close to $(*)$, though it is not quite the same. I'm currently looking for similar integrals that actually amount to $(*)$. I've already looked into numerous other integrals with powers of the integrand - often with logarithmic terms - but to no avail so far. In parallel to continuing on this path, I thought perhaps one could explore finding such an expression indirectly through Feynman diagrams.

My reasoning is as follows: if one could associate a Feynman diagram with expressions of the form $I_{k}$, then perhaps one could infer what kind of Feynman diagram should be associated with $S_{k}$, which in turn could yield information about the integral form that corresponds to $(*)$.

Questions:

  1. How does the integral $I$ arise in Feynman diagram calculations? Is there a unique Feynman diagram that corresponds exactly to this integral?
  2. Do integrals of the form $I_{k}$ also arise in Feynman diagram calculations? If so, how? Can one discern a pattern in the successive Feynman diagrams that are connected to $I_{1}, I_{2}, I_{3}, \dots$ ?
  3. Is it also possible to associate a Feynman diagram to values - in particular of the form $S_{k}$ - or do they only correspond to the integrals themselves?
$\endgroup$
2
  • 1
    $\begingroup$ Similar integrals are found when performing the Feynman parameter integrals found when doing loop calculations. Perhaps someone can show an example of how one gives rise to a specific polylogarithm related function though they tend to be quite messy and long. $\endgroup$
    – Triatticus
    Commented Jul 15, 2022 at 16:20
  • 1
    $\begingroup$ @Triatticus A specific example would be great indeed $\endgroup$ Commented Jul 16, 2022 at 11:42

1 Answer 1

3
$\begingroup$

For what it's worth, multiple polylogarithms (MPLs), similar to OP's title example, appear in multiloop Feynman diagrams of already scalar theories, see e.g. Ref. 1 for details.

References:

  1. C. Duhr, Mathematical aspects of scattering amplitudes, TASI lectures 2014, arXiv:1411.7538.
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.